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Published on: September 28, 2019
Bicarbonate enhances alpha-synuclein oligomerization and nitration: intermediacy of carbonate radical anion and
Christopher Andrekopoulos1, Hao Zhang, Joy Joseph
1Department of Biophysics, Free Radical Research Center, Medical College of Wisconsin, 8701 Watertown Plank Road, P.O. Box 26509, Milwaukee, WI 53226, USA.
Abstract:
alpha-Synuclein, a neuronal presynaptic protein, has been reported to undergo oligomerization to form toxic Lewy bodies in neurodegenerative disorders. One of the proposed mechanisms for aggregation of alpha-synuclein involves oxidative and nitrative modifications. In the present study, we show that addition of 3-morpholino-sydnonimine chloride (SIN-1) or slow infusion of pre-formed peroxynitrite (ONOO-) to mixtures containing alpha-synuclein and HCO3- markedly enhanced both nitration and aggregation of alpha-synuclein through dityrosine formation. Bicarbonate-dependent peroxidase activity of Cu,Zn-superoxide dismutase (SOD1) also induced covalent aggregation of alpha-synuclein via a CO3*--dependent mechanism. Nitrone spin traps completely inhibited CO3*--mediated oxidation/nitration and aggregation of alpha-synuclein. Conversely, alpha-synuclein inhibited CO3*--induced spin adduct formation. Independent evidence for CO3*--mediated oxidation and dimerization of alpha-synuclein was obtained from UV photolysis of [(NH3)5CoCO3]+, which generates authentic CO3*-. Irradiation of [(NH3)5CoCO3]+ and NO2- in the presence of alpha-synuclein yielded nitration and aggregation products that were similar to those obtained from a SIN-1 (or slowly infused ONOO-) and HCO3- or a myeloperoxidase/H2O2/NO2- system. Hydrophobic membranes greatly influenced alpha-synuclein aggregation and nitration in these systems. We conclude that both CO3*- and NO2* could play a major role in the nitration/aggregation of alpha-synuclein.
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